This invention relates to a novel process for polymerizing vinylpyridine. In particular, the invention is concerned with a process for the suspension polymerization of vinylpyridine catatyzed by a water-soluble free radical initiator in the presence of small particles of solid polyolefin.
Currently, polyvinylpyridine is blended with various isotatic polyolefins, e.g., polypropylene, to render the resulting mixture dye receptive. Blending is accomplished by mixing the solid polyolefin with the solid polyvinylpyridine and then extruding the mixture as a film or a filament. This process has the usual problems associated with solids mixing. Incomplete or poor mixing results in a dyed article having color streaks. Poorly mixed batches show streaks even after melting and extrusion. One problem in obtaining good mixing of these two solids is the difficulty in getting small-sized polyvinylpyridine particles.
Polyvinylpyridine is produced by the free radical catalyzed polymerization of either 2-vinylpyridine or 4-vinyl-pyridine or mixtures of the two. Both bulk and suspension processes have been used to effect this polymerization. The bulk polymerization process produces the usual solid mass of polymer which must be broken up and then further ground up in order to produce small-size particles for further handling. It is expensive to grind this polymer to a powder as fine as the polyolefin powder. Anything less results in poor mixing.
Surprisingly, the usual aqueous suspension polymerization of vinylpyridine also leads to large lumps of polymer. Although the monomer is comletely dispersed, the polymer clumps up during polymerization. Sometimes the lumps are large enough to interfere with the agitator. These lumps also stick to the wall of the reaction vessel and are difficult to remove from the reactor. After separation from the aqueous medium, the lumps are difficult to dry. Even then, the lumps of polymer suffer the same disadvantage as bulk polymer; namely, they must be ground up into a powder in order to permit complete mixing with a polyolefin powder.